Primary cell anode



June 1957 J. J. STOKES, JR 2,796,456

Y PRIMARY CELL'ANODE Filed Feb. 8, 1955 INVENTOR John J 570/183, :7".

ATTORNEY Unitedl Snares atent O PRIMARY CELL ANUDE John J. Stokes, Jr.,Unity, Pa., assigncr to Aluminum Company of America, Pittsburgh, Pa, acorporation of Pennsylvania Application February 8, 1955, Serial No.486,758

Claims. (Cl. l36ltll)) This invention relates to primary cells or" thedry type and more particularly to an aluminous metal anode which alsoserves as the container for the cell. The term aluminous metal as usedherein refers to both aluminum and those alloys which contain more than50% of that element.

One of the general objects of the invention is to provide an aluminousmetal dry cell container which has a longer shelf life than has beenobtained heretofore with aluminum containers. Another object is toprovide a container or can which ollers an improved cell performancewithout perforation of the container wall. Still another object is toprovide a dry cell container of composite construction in which the baseor supporting component closely resembles the anode alloy in electricalcharacteristics and hence if the anode is consumed or fails, thesupporting member can serve as the anodic component of the cell. Aparticular object is to provide a duplex aluminous metal dry cellcontainer which permits substantially complete consumption of the anodewithout perforation of the container wall. Other objects will beapparent in the following disclosure and from the drawings wherein Fig.1 is a somewhat diagrammatic View partly in section illustrating a drycell structure embodying the invention, and

Fig. 2 is an enlarged sectional view of a portion of the container wallillustrating its composite construction.

Primary cells having aluminum anodes have been proposed heretofore inorder to take advantages of the relatively high electrochemicalequivalent of aluminum as compared to that of zinc, the metalextensively employed heretofore in the construction of dry cells. Suchcells containing aluminum anodes, however, have suffered from at leasttwo drawbacks, namely, the accumulation of oxide film on the anode,especially if the cell is kept on the shelf for extended periods oftime, which interferes with quick response for current when placed in acircuit, and perforation of the cell wall either during service orduring storage if the common halides are used as the electrolyte. Myinventionis directed to overcoming these disadvantages and to usingaluminous metal in a more efiicient manner.

My invention broadly comprises the discovery that an improved dry cellcan be made by forming the container or shell from a composite aluminousmetal body wherein the inner portion in contact with the electrolyteconsists of a special aluminum base alloy and the second or outerportion is composed of aluminous metal of a different composition whichhas a lower electrode potential, i. e. it is less anodic toward thecathode than the inner layer. For opera-tion of the cell it is of coursenecessary to use an electrolyte which is adapted to serve in contactwith aluminum and aluminum base alloys. The special anode alloy which Ihave found to be superior to other aluminum base alloys not only gives ahigh output in closed circuit but permits storage in open circuitcondition without substantial loss in efficiency. The outer orsupporting alloy layer although slightly less eificient than the anodealloy can readily serve as the anode without any significant changein-the potential of the current supplied by the cell.

Various electrolytes, especially solutions, have been suggested for usein contact with aluminum anodes but I have found that superior resultsare obtained by employing aluminum chloride hexahydra-te and ammonium,sodium or potassium chromate in the cell paste incombination withmanganese dioxide and finely divided carbon. The improved electrolyteforms the subject matter of my co-pending application Serial No.486,757, filed on even date herewith.

Although aluminum can be used as the anode of a primary cell if theabove mentioned electrolyte is employed, I have found that much betterperformance is obtained over a longer period of time if the anodeconsists of analloy composed essentially of aluminum and at least onealloying component of the group consisting of 0.001 to 5% zinc, 0.02 to0.5% tin, 0.02 to 1% bismuth, 0.1 to 10% magnesium and 0.5 to 2% of theintermetallic compound MgzSi. Minor amounts of other elements such asboron, titanium, chromium and manganese may also be present inquantities usually employed in aluminum base alloys to impart somedesired property to the alloy. Under some circumstances it may even bedesirable to include a small amount of copper, less than 0.5%. For thesake of conve-niencethese alloys may be referred to as anode alloys. Acontainer made of one of these alloys is substantially uniformlyattacked over the entire inner surface by the electrolyte in the celland does not acquire a film which obstructs action by the electrolyte.Moreover, these alloy additions tend to increase the electrode potentialof the anode which, of course, is advantageous. Of the various alloys Iprefer the aluminumzinc composition and for optimum results an alloy ofaluminum of a purity of not less than 99.8% and from 0.5 to 1.5% zinc ispreferred.

While the several alloys mentioned above serve very well as a consumableanode shell or container fromjhe standpoint of current output, theysuffer from the disadvantage of being perforated if there is severelocal attack. To overcome this disadvantage and yet derive the desiredbenefits from the alloys, an outer layer or sheath of aluminous metal ofa 'difierent composition is provided which has a lower electrodepotential than the inner layer. Generally, this difference should amountto at least 0.1 millivolt and should be within the range of 0.1 to 200millivolts. Greater differences cause excessive consumption of the anodealloy. The alloys used for the outer layer must be chosen with respectto the electrode potential of the inner layer. The electrode potentialof a given alloy can be determined according to standard methods, forexample, by use of a calomel half cell and solution of the electrolyteto be used in the cell. Suitable alloys for the outer layer are suchwell known ones as the aluminum-manganese and aluminum-magnesiumsilicide types. In addition, commercially pure aluminum of 99.2% purity,and even aluminum of lower purity can be used for the outer layer.Alloys which can be readily worked and formed into containers arepreferred. An alloy which is preferred for the shell is one composed ofaluminum and from 0.5 to 1.5% manganese.

The composite aluminous metal container of my inven tion consists of arelatively thick inner layer of the anode alloy and a relatively thinouter layer of the less anodic metal. In general, the anode compositionshould constitute as large a proportion, not less than half, of thetotal thickness of the shell wall as is practicable, usually within therange of 50 to of the total thickness. According to my preferredpractice the inner layer should 3 constitute from 60 to 80% of the totalthickness of the composite shell.

In operation of the cell the anode alloy is gradually consumed and whenany pits develop which extend through the inner alloy layer and reachthe outer layer they become enlarged by spreading laterally rather thanperforating the remainder of the container wall. This behavior of theinner layer is brought about by creating and maintaining a difference inelectrode potential between the two components, the inner alloy layerhaving the higher potential. it the cell is kept in service until theanode alloy has largely disappeared, the cell can still deliversubstantially the same current for a short period of time. \In thisrespect, my composite shell difiers from any duplex cell containerswhich have been proposed heretofore. It also means that the maximumoutput of the cell is obtained over a longer period of time becauseperforation of the shell does not occur until a major portion of theanode has been consumed.

The composite shell or container should have a wall thickness equivalentto that employed in the dry cell art where zinc is used. For small cellssuch as used in flashlights, the shell may be from 0.010 to 0.015 inchin thickness Whereas in larger shells, such as the common No. 6 size,the wall may be 0.018 to 0.020 inch in thickness. Of course, a heaviershell may be employed but this must be balanced against the amount ofelectrolyte present in the paste mixture.

The composite material from which the container or shell is formed maybe fabricated in any conventional manner. For example, sheets or slabsof the two alloys may be bonded together by hot rolling, or one alloymay be cast against a slab of the other one and the resulting body hotrolled. Still another method is that of spraying the anode alloy uponthe outer or supporting layer. Still another method of fabrication isthat of producing the containers or cups from composite slugs by theimpact extrusion process. The forming of the containers from sheetproducts may be accomplished in conventional manner such as by drawing.In all cases it is important that the anode alloy be firmly bonded tothe supporting member and thereby avoid any separation or scaling duringthe operation of the cell.

Referring to Fig. 1 which illustrates one embodiment of my invention, itwill be seen that a composite cylindrical shell 1 consisting of an inneranode layer 2 and an outer layer 3 is lined with an inert absorbentpaper 4, the top edge of which is crimped inwardly to assist inretaining the paste in position. The paper layer serves to preventdirect contact of the mix with the shell yet is permeable to theelectrolyte. .A conventional carbon rod 5 centrally disposed in theshell is the cathode. Between the paper lined shell and the carbon rodis the paste 6 containing the electrolyte, depolarizer and finelydivided carbon. Above the paste is a space 7 which can accomm-odate anyexpansion of the paste that may occur without rupturing the cell wall orthe top seal. The cell is sealed by a suitable plastic or resinoussubstance 8 in asso ciation with a fibrous separator 9. The carbon rod 5is provided with a conventional metal cap 10 to insure good electricalcontact with another metallic conductor.

In the enlarged View of a portion of the cell wall shown in Fig. 2, theduplex character of the aluminous metal container wall is plainlyevident. The inner layer 2 of the anode alloy is much thicker than theouter layer 3. The paper liner 4 in contact with the inner layer 2 andthe electrolyte paste 6 are also shown.

For many purposes it is desirable to provide a paper or other insulativecover for the cell. Such covers are well known and need not bedescribed.

It will be appreciated that the primary cells which may employ thecomposite shell described above may vary considerably in size. Thecomposite shell has been found to be especially useful for theproduction of small cells of the type used in flashlights and similararticles.

The improvement gained from the use of a composite shell as compared toa shell of a single composition is illustrated in the following example.Flashlight cells were made which were identical except as to the composition of the shells. Each cell had a carbon rod cathode and anelectrolyte paste composed of aluminum chloride hexahydrate andpotassium chromate in equal parts, manganese dioxide, carbon black andwater. The shell in one case consisted of aluminum of 99.8% purity andthe other shell was of the composite type, the inner layer constituting70% of the total thickness of the shell wall and composed of analuminum-zinc alloy made from 1% zinc and aluminum of 99.8% purity, andthe outer layer composed of an aluminum base alloy consisting ofaluminum and 1.25% manganese, the two layers having been bonded by hotrolling them together. In a shelf life test the first type of cellexhibited perforation of the shell in eight months Whereas no failureoccurred in the second type after a fourteen month storage.

Having thus described my invention and an embodiment thereof, I claim:

1. A primary cell of the dry type comprising a cathode, an electrolyteand a composite aluminous metal container as the anode, said containerconsisting of two metallic layers of different composition, the innerlayer in contact with the electrolyte constituting more than half thetotal wall thickness of the shell, said inner layer also consisting ofan alloy composed essentially of aluminum and at least one alloyingcomponent selected from the group consisting of 0.001 to 5% zinc, 0.02to 0 .5% tin, 0.02 to 1% bismuth, 0.1 to 10% magnesium and 0.5 to 2% ofthe intermetallic compound MgzSi, and the outer layer composed ofaluminous metal having an electrode potential below that of the inneralloy layer, said layers being firmly bonded together.

2. A primary cell of the dry type comprising a cathode, an electrolyteand a composite aluminous metal container as the anode, said containerconsisting of two metallic layers of different composition, the innerlayer in contact with the electrolyte constituting from 50 to of thetotal wall thickness of the shell, said inner layer also consisting ofan alloy composed essentially of aluminum and at least one alloyingcomponent selected from the group consisting of 0.001 to 5% zinc, 0.02to 0.5% tin, 0.02 to 1% bismuth, 0.1 to 10% magnesium and 0.5 to 2% ofthe intermetallic compound MgzSi, and the outer layer composed ofaluminous metal having an electrode potential at least 0.1 millivoltbelow that of the anode alloy of the inner layer, said layers beingfirmly bonded together.

3. A primary cell of the dry type comprising a cathode,

an electrolyte and a composite aluminous metal container as the anode,said container consisting of two metallic layers of differentcomposition, the inner layer in Contact with the electrolyteconstituting from 50 to 90% of the total wall thickness of the shell,said inner layer also consisting of an aluminum-zinc alloy composed of0.001 to 5% zinc and aluminum of a purity not less than 99.8%, and theouter layer composed of an aluminous metal having an electrode potentialat least 0.1 millivolt below that of the aluminum-zinc alloy, saidlayers being firmly bonded together.

. 4. A primary cell of the dry type comprising a cathode, an electrolyteand a composite aluminous metal container as the anode, said containerconsisting of two metallic layers of different composition, the innerlayer in contact with the electrolyte constituting not less than halfthe total Wall thickness of the shell, said inner layer also consistingof an aluminum-zinc alloy composed of 0.5 to 1.5% Zinc and aluminum of apurity not less than 99.8%, and the outer layer composed of an aluminumbase alloy consisting of aluminum and 0.5 to 1.5% manganese, said layersbeing firmly bonded together.

5. A primary cell of the dry type comprising a cathode, an electrolyteand a composite aluminous metal container as the anode, said containerconsisting of two metallic layers of difierent composition, the innerlayer in contact with the electrolyte constituting from 60 to 80% of thetotal wall thickness of the shell, said inner layer also consisting ofan aluminum-zinc alloy composed of 0.5 to 1.5% zinc and aluminum of apurity not less than 99.8%, and the outer layer composed of an aluminousmetal having an electrode potential below that of the aluminumzincalloy, said layers being firmly bonded together.

References Cited in the file of this patent UNITED STATES PATENTS

